Abstract:

In the process of tailing cemented filling goaf，the discontinuity of the filling operation causes delamination of the filling body at the interface of the two fillings.In order to study the mechanical properties of the layered tailing cemented backfill and improve the deterioration effect of stratification，three types of delaminated backfill specimens，namely，intact non-delaminated，interface natural delamination，and interface sandblasted delamination，were produced.Each delamination type contains three material ratios of 1∶4，1∶6，and 1∶8 for ash-sand ratio，and uniaxial compression tests were conducted on specimens at curing ages of 3 d，7 d，14 d and 28 d to compare and analyze the deformation and damage characteristics of specimens with different delamination characteristics，different material ratios，and different curing ages.The results show that：（1） The delamination phenomenon significantly affects the mechanical properties of the tailing sand cemented backfill，considerably reducing the uniaxial compressive strength and the elastic modulus.Comparing the intact unstratified，naturally stratified specimens，the strength reduction rate caused by stratification increase ranged from 1.41% to 19.09% and exponentially with the increase of the curing age and ash-sand ratio.It indicates that the more significant the ash-sand proportion and the longer the maintenance age，the more pronounced the weakening effect of delamination of the backfill.Comparing the naturally delaminated and sandblasted delaminated specimens，the strength gain rate due to sandblasted delamination ranges from 1.92% to 16.26%，which increases with the increase of the ash-sand ratio，decreases firstly with the rise of the curing age and then remains flat and stable，and shows a higher strength gain rate in the early curing period.（2） The modulus of elasticity of the three-layered backfill types increases exponentially with the maintenance age.The discount of the modulus of elasticity of the natural layering relative to the complete layering increases with the rise in the maintenance age and decreases with the decrease of the gray sand ratio.The modulus of elasticity of the sandblasted layering relative to the natural layering only has a relatively apparent increase at 3 d，and the rest of the age is basically at the same level.（3） Using the rate of decrease of the post-peak strength curve as the ductility evaluation criterion，the post-peak strength curves of the three-layered types of backfill show better post-peak ductility with the decrease of ash-sand ratio，and it becomes more and more evident with the increase of maintenance age.The post-peak ductility performance of different layered types of backfill is in the order of interface sandblasted layered>interface natural layered>complete non-layered.（4）The damage of the delami-nated backfill is mainly in the form of tensile damage and conjugate shear damage，and the delamination surface makes part of the vertical compressive stress transformed into horizontal tensile stress，and the cracks inside the specimen are concentrated in the soft delamination surface，which makes the compressive strength of the backfill reduced.Sandblasting treatment can improve force transmission on the delamination surface to a certain extent.In order to reduce the degradation of the material’s mechanical properties by delamination，sandblasting，and other roughening treatment can be carried out on the last filling surface at the interval of the second filling.

Key words: tailing sand cemented backfill, characteristics of delamination, interface treatment, mechanical property, post-peak ductility, damage form